Typically, a navigation device is configured to display an image consisting of a map view generated from a digital map, and superposed with route information depicting a navigation route. The route information may be pre-recorded, but typically it is the result of a route-planning algorithm executed by the navigation device using suitable software. The navigation device may also include a position determining system (such as Global Positioning System (GPS)) for determining the current real-time position of the navigation device, and for dynamically adjusting the map view in accordance with the determined current position. Various types of map views are known including:
(i) A two-dimensional-based mapview that includes information in two-dimensions at ground level. For example, roads and buildings are represented by the shape of their footprints on the ground. Such two-dimensional information may be viewed as a plan (i.e. looking vertically downwardly on the map, in the same manner as a traditional paper map), or in artificial perspective as if viewing a traditional flat paper map from a perspective angle. However, in either case, the map view is “flat” in the sense that the information is only two-dimensional ground level information.
(ii) A three-dimensional-based perspective elevation view in which one or more digital map features or objects are presented in three dimensions. For example, a building is depicted showing the building's facades and a building height, which is a closer representation to the real world.
Many users find a three-dimensional perspective elevation view to be more intuitive than a two-dimensional flatview, especially when viewing the map at a relatively large display scale and/or for a built-up area during navigation. This is because the three-dimensional perspective and height information of objects depicted in the display more closely resembles these features as seen by the eye. For example, a person walking or driving at ground level sees building facades of certain height, rather than an abstract footprint of the building on the ground. The three-dimensional perspective information may therefore provide many users with more intuitive visual cues that aid the user to matching the display to what the user is seeing, and to follow the navigation route.
The above is especially true for a portable navigation device (PND), such as for handheld or in-vehicle use. In the case of in-vehicle use, a highly intuitive navigation display is desired that (i) provides the driver with current navigation information, (ii) provides an indication of the future route, so that driver can drive and position the vehicle appropriately, and (iii) avoids burdening the driver's attention, in order to allow the driver to drive the vehicle safely.
While a three-dimensional perspective elevation view is desirable for its intuitiveness, it can nevertheless result in additional display complications in terms of what the user is able to see in the map view. For example, the amount of three-dimensional information depends on the elevation angle at which the map view is generated. An elevation angle of 90 degrees corresponds to looking vertically downwards on to the map (as a two-dimensional plan), and so there is no three-dimensional perspective of each map object, and no obscuring of one map object in front of another. As the elevation angle is decreased, the map objects take on increasing three-dimensional height and form, and the amount of perspective increases. A tall map object, such as a building, may obscure another item of map information in the display, such as a lower building or a road at ground level. This situation could be remedied by increasing the elevation angle, until such obscuring no longer occurs, but this would necessarily reduce the amount of three-dimensional information in the view, and thereby reduce the benefit in terms of the intuitiveness of the view.
The present invention has been devised to address these contradictory issues.